Two challenges in the implementation of enzyme induced carbonate precipitation(EICP) are the cost of enzyme and the variability of the enzyme. Urease enzyme costs can be lowered drastically with the use of crude extract from plant materials, but experience has shown variability in the source of the crude urease enzyme, the crude urease enzyme extraction methods, and the concentration of the EICP solution can cause significant variability in the efficacy of the EICP solution. This thesis examines the variability in the efficacy of crude enzyme derived from jack beans (Canavalia ensiformis) and sword beans (Canavalia gladiata), two of the most commonly used sources of urease enzyme for EICP. The sources of variability investigated herein include the crude extraction method (including the effect of the bean husks on extraction) and different chemical constituent concentrations. These effects were assessed using enzyme activity measurements and precipitation efficiency tests. The activity tests were performed via spectrophotometry using Nessler's reagent. The precipitation tests looked at the influence of chemical constituent concentrations of 0.67 M calcium chloride and 1 M urea with non-fat dry milk in the EICP solutions and a higher concentration solution with chemical constituent concentrations of 2 M for both calcium chloride and urea with non-fat dry milk. The high concentration solution was selected based on preliminary testing results to maximize carbonate precipitation in one cycle of treatment. Significant sources of a decline in activity (and increase in variation) of the crude urease enzyme were found in extraction from sword beans with husks, high chemical constituent concentrations, and juicing instead of cheesecloth filtration. This thesis also examines the accuracy of commonly used correlation factors for converting electrical conductivity to urease enzyme activity. Crude jack bean and sword bean urease enzyme activity measurement via electrical conductivity was found to have a correlation coefficient that differed from the previously reported correlation when compared to activity measured via the more accurate spectrophotometry using Nessler’s reagent measurements.

Enzyme-induced carbonate precipitation (EICP) is a biogeotechnical soil improvement method that involves the precipitation of calcium carbonate via hydrolysis of urea (ureolysis) catalyzed by free urease enzyme in a calcium chloride solution. When this reaction takes place in the pore space of a sand, the precipitated calcium carbonate may bind soil grains together, thereby improving strength. Three studies on EICP are presented in this dissertation. In the first study, chemical equilibrium modeling via PHREEQC is used to develop a method for evaluating urease activity from electrical conductivity (EC) measurements in a closed reactor containing urea and urease. It is shown that a commonly used correlation to estimate urease activity from EC measurements overestimates the initial urea hydrolysis rate (thereby overpredicting the urease activity as well). In the second study, the crystal structure and mechanical properties of calcium carbonate minerals formed by EICP are studied. It is shown that a “modified” precipitate synthesized by the inclusion of nonfat dry milk in the EICP solution is more ductile than a “baseline” precipitate synthesized from an EICP solution without nonfat milk. Additionally, in sands biocemented using the modified EICP solution, precipitation occurs preferentially at the grain contacts. This may contribute to relatively high unconfined compressive strengths at low carbonate contents in some EICP-treated sands. The third study discusses the role of some sand characteristics on the strength following modified EICP treatment. Three batches of Ottawa 20-30 sand from different sources were treated identically using the modified EICP solution. Subsequent testing showed large differences in their unconfined compressive strengths. It is shown that this variation in unconfined compressive strength is due to differences in the surface microtexture and surface mineralogy of the sands.The fundamental studies presented in this dissertation provide a deeper understanding of some aspects of the EICP process.

Urease, an amidohydrolase, is an essential ingredient in the emerging engineering technique of biocementation. When free urease enzyme is used this carbonate precipitation process is often referred to as enzyme induced carbonate precipitation (EICP). To date, most engineering applications of EICP have used commercially available powdered urease. However, the high cost of commercially available urease is a major barrier to adoption of engineering applications of EICP in practice. The objective of this dissertation was to develop a simple and inexpensive enzyme production technique using agricultural resources. The specific objectives of this dissertation were (i) to develop a simple extraction process to obtain urease from common agricultural resources and identify a preferred agricultural resource for further study, (ii) to reduce the cost of enzyme production by eliminating the use of a buffer, centrifugation, and dehusking of the beans during the extraction process, (iii) investigate the stability of the extracted enzyme both in solution and after reduction to a powder by lyophilization (freeze-drying), and (iv) to study the kinetics of the extracted enzyme. The results presented in this dissertation confirmed that inexpensive crude extracts of urease from agricultural products, including jack beans, soybeans, and watermelon seeds, are effective at catalyzing urea hydrolysis for carbonate precipitation. Based upon unit yield, jack beans were identified as the preferred agricultural resource for urease extraction. Results also showed that the jack bean extract retained its activity even after replacing the buffer with tap water and eliminating acetone fractionation, centrifugation, and dehusking. It was also found that the lyophilized crude extract maintained its activity during storage for at least one year and more effectively than either the crude extract solution or rehydrated commercial urease. The kinetics of the extracted enzyme was studied to gain greater insight into the optimum concentration of urea in engineering applications of EICP. Results showed higher values for the half-saturation coefficient of the crude extract compared to the commercial enzymes. The results presented in this dissertation demonstrate the potential for a significant reduction in the cost of applying EICP in engineering practice by mass production of urease enzyme via a simple extraction process.